Hi, I am using following code to create appointment items in Outlook: private Microsoft.Office.Interop.Outlook.Application _Application; _AppointmentItem oAppointmentItem = (_AppointmentItem)m_Application.CreateItem(OlItemType.olAppointmentItem); When i try to cast the object to _AppointmentItem type (2nd line)it throws following exception: Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.Office.Interop.Outlook._AppointmentItem'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00063033-0000-0000-C000-000000000046}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)) Any idea why this code doesn't work on some machines with Outlook2003?